1. Field of the Invention
The present invention relates to a non-linear optical device for obtaining light of a shorter wavelength, utilizing a non-linear optical effect.
2. Related Background Art
There has conventionally proposed a device for generating harmonic waves in order to obtain light of a shorter wavelength. Such device is schematically shown in FIG. 1.
In FIG. 1, a basic wave 32 of an angular frequency .omega. emitted from a semiconductor laser 31 enters a non-linear optical crystal 30 composed, for example, of LiNbO.sub.3 or KDP, thereby generating a harmonic wave 34 of an angular frequency 2.omega., together with a transmitted wave 33 of the angular frequency .omega..
Also for modulating such harmonic wave, there is already known a device as shown in FIG. 2, in which the same components as those in FIG. 1 are represented by the same numbers and will not be explained further. In said device, the non-linear optical crystal is replaced by a polar macromolecular material 35, to which a bias field is applied by a power source 38, with modulation by a modulator 39. When the bias field is turned on, the molecules of said polar macromolecular material 35 are aligned in a same direction, whereby the non-linear receptivity .chi..sup.(2) is elevated to generate the harmonic wave 34. When the bias field is turned off, the orientation of the molecules is thermally disturbed to reduce .chi..sup.(2), whereby the harmonic wave 34 is decreased.
However these devices have been associated with following drawbacks;
1) Efficiency of harmonic wave generation is low, due to low non-linear receptivity .chi..sup.(2) ;
2) It is difficult to prepare such device in combination with a light-emitting device such as a semiconductor laser, on a same substrate;
3) In case of the device shown in FIG. 1, the non-linear optical crystal of satisfactory quality is costly to prepare; and
4) In case of the device shown in FIG. 2, the response is as low as several milliseconds, as it is determined by the orientation by molecular rotation by the bias field.